1. Field of the Invention
The present invention relates to a forming method and a forming apparatus of nanocrystalline silicon structure with oxide or nitride termination, and more particularly to a forming method and forming apparatus of nanocrystalline silicon structure carried out by using dry processes only.
2. Description of Related Art
A nanocrystalline silicon structure with oxide or nitride termination is composed of a large number of silicon single crystals which have a grain size of 10 nm or less and are terminated with oxygen or nitrogen. Since the nanocrystalline silicon structure shows unique physical phenomena as to electron confinement, photoluminescence and electron emission, it has been noticed for its possibility of application to a variety of devices such as a single electron memory LSI, an optical interconnection LSI, a light emitting device and a lightweight, large screen display panel.
The nanocrystalline silicon structure has been mainly prepared by two methods. In the process of forming silicon single crystal grains, one method employs an anodic oxidation treatment, and the other method employs an annealing treatment of, for example, an amorphous silicon nitride film having stoichiometrically excessive silicon to precipitate silicon single crystal grains.
In the former method, as described in JP2003-86093A, a polycrystalline silicon film is deposited on a substrate by using CVD method (Chemical Vapor Deposition), then annealed, and anodically oxidized in a hydrogen fluoride solution to form single crystal grains. That is, the polycrystalline silicon is partially etched in the anodic oxidation treatment to prepare the nanocrystalline silicon structure comprised of a large number of nanoscale silicon crystal grains. After the anodic oxidation, the surfaces of crystal grains are electrochemically treated, for example, in sulfuric acid to terminate crystal grains with oxygen. Thus, the nanocrystalline silicon structure with oxide termination is prepared. As mentioned above, since the polycrystalline silicon is partially etched to form crystal grains, the silicon structure thus prepared is porous and therefore referred to as a porous silicon.
In the latter method described in, for example, JP2000-273450A, an amorphous silicon nitride film is formed on a substrate by using CVD method. Here, the ratio of a material gas such as monosilane (SiH4) gas to ammonia (NH3) gas is adjusted so that the amorphous silicon nitride film has a stoichiometrically excessive amount of silicon atoms; i.e., x<4/3 in SiNx. Then, the film is annealed to precipitate nanoscale silicon crystal grains. Thus, the nanocrystalline silicon structure with nitride termination is prepared. When an SiOx film is formed instead of SiNx, the nanocrystalline silicon structure terminated with oxygen is similarly prepared.